The present invention relates to a differential signal reception device and method for supporting variable threshold levels.
Differential signaling is widely used to communicate voltages between integrated circuits or systems because of the benefit of removing common-mode noise. In digital data communications systems that employ differential signaling, both inputs are typically given to a differential input limiting amplifier to decide the logic level of the input signal. This limiting amplifier will have a logic high if the true input is higher in voltage than the negated input. The function of a limiting amplifier allows the device to have higher performance than a linear amplifier. That function is to drive the output as hard as it can any time the true input is higher than the negated input.
This is a high-performance way to decide the logic level of the signal, as differential input limiting amplifiers having non-linear gain are commonly available with much higher bandwidths than linear amplifiers. An alternative way to achieve this function is to put the two differential inputs into a differential linear amplifier which will create the analog xe2x80x9cdifferencexe2x80x9d signal and then to send this xe2x80x9cdifferencexe2x80x9d signal to a logic comparator that will output a logic true if the xe2x80x9cdifferencexe2x80x9d is positive and a logic false if the xe2x80x9cdifferencexe2x80x9d is negative. This alternative is limited by the bandwidth of the linear amplifier used.
The present invention relates to a differential signal reception device and method for supporting variable threshold levels.
It is an object of the present invention to flexibly make an input to this decision circuit appear to an outside driving circuit as if the decision circuit were a purpose-built input network supporting a fixed impedance input into either a floating or fixed DC termination voltage. It is also an object of the present invention to further allow the internal decision process to support a variable threshold level when deciding logical 1/0 values and to attenuate the users input signal range for the purpose of making sure the range of the user""s signals does not exceed the operating range of readily available decision circuit (limiting amplifier) integrated circuits.
In one embodiment, the differential signal reception device according to the present invention includes means for receiving an input differential signal from a differential signal source, a variable threshold voltage, and a termination voltage from a controller (e.g. a computer); a variable decision threshold means for providing a variable decision threshold voltage corresponding to level shifts of the threshold voltage; and a differential limiting amplifier responsive to the threshold means for switching between high or low states.